1. Field of the Invention
The invention relates to a torque sensor and an electric power steering system.
2. Description of Related Art
Japanese Patent Application Publication No. 2010-237082 (JP 2010-237082 A) proposes a technique of disposing a torque sensor and an index sensor coaxially with a steering shaft in an electric power steering system. The torque sensor is disposed on the steering shaft that couples a steering operation member and a steering mechanism. The index sensor detects the number of rotation of the steering shaft that rotates multiple times. The torque sensor has a first magnetic sensor disposed beside a first magnet unit. The index sensor has a second magnetic sensor disposed beside a second magnet.
In JP 2010-237082 A, a plate member formed of a magnetic body is provided between the first magnetic sensor and the second magnet. The plate member reduces a magnetic flux radiated from the second magnet toward the first magnetic sensor. Therefore, the magnetic interference of the index sensor with the torque sensor is reduced, and the detection accuracy of the torque sensor can be enhanced. However, the plate member and a structure that supports the plate member are required, and thus the number of components and the number of assembly steps increase and the manufacturing cost increases.